The cochlea is an organ in the inner ear that converts sound vibrations into electrical signals, and the electrical signals are transmitted to the brain by the auditory nerve. The cochlea has a scala tympani, scala media, and a scala vestibule, which are fluid-filled ducts separated by a tapered membrane called the basilar membrane. As shown in FIG. 1, mechanical impedance changes along the basilar membrane typically causes tonotopic filtering along the length of the basilar membrane allowing high frequency sounds to resonate near the base of the cochlea and lower frequency sounds to travel through the cochlea and resonate near the apex of the cochlea.
The organ of Corti is supported by the basilar membrane and houses sensory cells of the cochlea. Typically, a patient with sensorineural hearing loss has malfunctioning or nonexistent sensory cells housed by the organ of Corti, but has a functioning auditory nerve. Cochlear implants are often used to replace these malfunctioning or nonexistent sensory cells.
Cochlear implants typically have the ability to restore 80 to 90% of word recognition hearing in a patent having sensorineural hearing loss. An example of a traditional cochlear implant is shown in FIGS. 2A, 2B, and 2C. This traditional cochlear implant is powered by a battery and includes an external microphone and an external sound processing unit positioned behind the ear (FIG. 2A). The traditional cochlear implant further includes an inductive link that transmits power and information from an external unit to a receiving unit disposed in subcutaneous tissue of the ear (FIG. 2B). Further, a probe with a flexible silicone shank having an array of platinum or platinum-iridium electrodes and two ground electrodes is inserted into the cochlea (FIG. 2C). The probe is typically surgically implanted into the scala tympani of the cochlea, and is wound through the cochlea.
Traditional cochlear implants, such as the cochlear implant described above with reference to FIGS. 2A, 2B, and 2C, typically have an undesirably large power consumption (e.g. the battery may last up to only about 5 days), has high latency, is relatively expensive, and the probe is difficult to insert into the cochlea. Additionally, due to the inflexibility of the probe, the basilar membrane may get punctured during implantation of the probe into the cochlea which can further damage hearing loss. The cochlear implants that are currently available are also often difficult for use in sporting activities and under water (such as in a shower).
Fully implantable cochlear implants have been studied. However, none of these fully implantable cochlear implants achieve a desired sensitivity and none are easy to implant into the curved cochlea.
Accordingly, there remains an opportunity to develop an implantable cochlear implant that is flexible in the plane of curvature of the cochlea and is implantable without damaging the basilar membrane.